是否可以在noexcept规范中使用`this`? [英] Is `this` allowed inside a noexcept specification?

问题描述

我有一些代码要求我使用*this，但我希望它不友好:

I have some code which requires me to use *this, but I want it to be noexcept friendly:

struct foo;

// Would actually be something with conditional noexcept
void do_something(foo&);

struct foo {
    void fn()
        noexcept(noexcept(::do_something(*this)))
    {
        ::do_something(*this);
    }
};

但是， gcc拒绝了:

<source>:7:43: error: invalid use of 'this' at top level
         noexcept(noexcept(::do_something(*this)))

如果我只是访问成员，则gcc可以:

If I just access a member, gcc is fine:

void do_something(int);

struct bar {
    int x;

    void fn()
        noexcept(noexcept(::do_something(x)))
    {
        ::do_something(x);
    }
};

但是，如果我通过this指针访问该成员，则 gcc再次抱怨:

However, if I access the member through the this pointer, gcc complains again:

struct baz {
    int x;

    void fn()
        noexcept(noexcept(::do_something(this->x)))
    {
        ::do_something(this->x);
    }
};

诊断:

<source>:7:42: error: invalid use of 'this' at top level
         noexcept(noexcept(::do_something(this->x)))

我尝试过的所有其他编译器在noexcept规范内使用this接受，但是我没有实际上知道是gcc出现了错误还是所有其他编译器.

Every other compiler I tried accepts using this inside the noexcept specification, but I don't actually know if it's gcc that has the bug or all the other compilers.

可以在noexcept规范内使用关键字this吗?

Can the keyword this be used inside a noexcept specification?

推荐答案

是的，它是允许的. [expr.prim.this] p2 说:

Yes, it is allowed. [expr.prim.this]p2 says:

如果声明声明了类X的成员函数或成员函数模板，则表达式this是类型为指向 cv-qualifier-seq X的指针"的prvalue.在可选的 cv-qualifier-seq 和功能定义的末尾之间，[...].

If a declaration declares a member function or member function template of a class X, the expression this is a prvalue of type "pointer to cv-qualifier-seq X" between the optional cv-qualifier-seq and the end of the function-definition, [...].

cv-qualifier-seq 是指成员函数的cv限定词，

The cv-qualifier-seq refers to the cv qualifiers of the member function, which appear before the noexcept specifier:

parameters-and-qualifiers:
    ( parameter-declaration-clause ) cv-qualifier-seq[opt] ref-qualifier[opt] 
      noexcept-specifier[opt] attribute-specifier-seq[opt]

因此，this是在 noexcept-specifier 中使用的有效表达式.这是gcc未实现的DR( cwg1207 ). 错误报告.

So, this is a valid expression to use in the noexcept-specifier. This was a DR (cwg1207), which gcc doesn't implement. The bug report.

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